text: As far as I know, there is non such thing. But what you aim for should be fairly straight forward to implement, as long as you happen to have some experience with C++.
  
  
  Locate the circleSet in the OpenFOAM source directory.
  Make a local copy of it and rename it to something like faceSetSet.
  Read the name of the faceSet you'd like to sample on.
  Read the faceSet.
  In each timestep, loop only over those faces and average the fields you'd like.
  
  
  This is a very rudimentary and basic algorithm, you'd have to fill in the gaps. If you need more help, let me know.